1. Field of the Invention
This invention relates to a receiver having a preset tuner and, more particularly, to a receiver that counts the number of receivable channels in order to determine whether a signal is within a terrestrial-wave television broadcast channel plan or within a CATV broadcast channel plan.
2. Description of the Prior Art
Receivers of this kind are disclosed, for example, in Japanese Laid-open No. 87415/1995 (H04N5/44, 7/16) laid open on Mar. 31, 1995; U.S. Pat. No. 4,776,038; Japanese Patent Laid-open No. 184301/2000 (H04N5/44, 5/02, 7/18) laid open on Jun. 30, 2000, among others (and so on). This prior art can determine whether broadcast channels are within a CATV channel plan by detecting the presence of (a plurality of) particular CATV channels, in an automatic determination as to whether they are within a terrestrial-wave television broadcast (hereinafter, “TV” or “TV broadcast”) or within a CATV broadcast.
The prior art, however, can do nothing more than count the number of receivable channels from a range of particular CATV channels in which spurious signals or “ghosts” are not taken into consideration. That is to say, where many channels are present, it may happen that the sum or difference frequency between two particular frequencies falls under and is received by the broadcast station (ghost) having a certain frequency range or the incorrect reception results due to spurious reception. In the prior art, there has always existed the possibility of miscounting, which can in an incorrect determination.
Furthermore, the present applicant has proposed, in Japanese Utility Model Registration No. issued on May 12, 2000, a novel method for resolving this problem. The method proposed is to determine whether the channel frequency of each reception is within a certain frequency range within the center frequency. If it is within a predetermined frequency range, it is counted as a receivable channel.
This method reduces the miscounting due to “ghosts” or spurious signals, but cannot completely preclude such miscounting.